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    Ramjet vs Scramjet propulsion SAMs

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    Austin

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    Ramjet vs Scramjet propulsion SAMs

    Post  Austin on Mon Jun 11, 2012 10:48 am

    Why arnt Ramjet based propulsion popular with SAM as they were in 60's with SA-6 and Indian Akash now.

    It offers propulsion all the way flight which is no coasting like solid fuel missile , low volume/weight because they need not carry oxidiser  and offers decent speed with no drop down in speed in its entire flight.

    Why arnt Russian or US missile designers not working on Ramjet propulsion , while AAM are now turning back to it.
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    GarryB

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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  GarryB on Tue Jun 12, 2012 10:26 am

    I suspect ramjet propulsion was caught up in many cases by solid fuel rocket propulsion, which turned out to be less bulky and offered higher peak speeds and better acceleration... remember ramjets require rockets and ramjets.

    When scramjet technology is mastered I suspect a shift back to scramjet technology, but there are penalties for ramjet designs including large internal areas for piping and airflow and combustion. In missiles like SA-6 and Kh-31 and Onyx the large empty space is taken up by the solid fuelled rocket used to accelerate the missile to a speed where the ramjet can be started and operated efficiently.

    For air to air missiles having terminal manouvering performance is much more important than for many other types of missile because aerial targets can manouver in 3D space making interception more complicated.

    For anti ship missiles solid fuel simply doesn't allow the range needed for a decent anti ship missile, so if you want supersonic performance your choice is dangerous liquid fuel rocket with a throttle like Kh-22M or Kh-32, or a ramjet/scramjet arrangement. The one high speed solid fuelled rocket anti ship missile is the Kalibre and only uses the solid rocket for the last phase of the engagement over a relatively short distance. This is possible because ships don't move very far very fast... a carrier operating at 45 knots can't turn on the spot and would be detectable from very long ranges so a long flight time is not a problem... unless it is hours...


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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  medo on Wed Jun 13, 2012 4:38 pm

    I also think it depend on altitudes, for which missile is meant to operate. In low altitudes there is enough oxygen in the air to operate with ramjet engine in high speeds, but in higher altitudes or in space there is little or no oxygen to operate with ramjet engine, so solid fuel rocket engine is better for task.
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    GarryB

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    Why arnt Ramjet based propulsion popular with SAM as they were in 60's with SA-6 and Indian Akash now.

    Post  GarryB on Thu Jun 14, 2012 6:50 am

    There is still oxygen at high altitude for combustion, the problem for humans breathing is largely of the inefficiency of the human lung.

    A Ramjet powered missile zipping along at mach 6 will be scooping up several kilometres of air per second... combustion shouldn't really be an issue... certainly to 30km altitude or more.

    Oxygen concentrations would only become a problem at perhaps 50km or higher.

    Of course with any jet engine there are problems with sharp turns where flameouts and stalls might become a problem.

    The key advantage of Ramjets is the throttle where a high throttle setting will allow the weapon to climb and accelerate but once it gets to altitude the throttle setting can be reduced to extend range, while closer to the target area the throttle can be opened up again to increase terminal manouver capability.

    The ability to chance the throttle setting on older missiles was less important but a modern missile with a digital navigation system with a range of flight profile options and fairly smart attack capabilities could utilise the flexibility of the ramjet propulsion and increase speed and flight range.


    With a superior scramjet motor of course performance increases further so new speeds can be achieved... in fact a smart flight management system will become necessary to potentially prevent the missile accelerating during flight as it uses up fuel and gets lighter and faster to prevent it accelerating to too high a speed and being damaged from the heat of friction....


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    TR1

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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  TR1 on Wed Nov 28, 2012 10:20 am

    Question- was there ever any thought of adding ramjet propultion to the S-300 family? Presumably to help maintain speed throughout the envelope....
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    SOC

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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  SOC on Wed Nov 28, 2012 8:59 pm

    TR1 wrote:Question- was there ever any thought of adding ramjet propultion to the S-300 family? Presumably to help maintain speed throughout the envelope....

    Not that I've heard about, and I've investigated the development of the system pretty extensively. I think there was a rumor of ramjet propulsion being considered for the "40N6" at some point, but not for any of the S-300 missiles. An up-and-over flight profile does help to mitigate velocity loss after burnout to a degree. At any rate the missile retains enough kinetic energy at endgame to get the job done.
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    Question- was there ever any thought of adding ramjet propultion to the S-300 family? Presumably to help maintain speed throughout the envelope....

    Post  GarryB on Wed Nov 28, 2012 9:45 pm

    The speed the missile travels at it would need to be scramjet propulsion, and unfortunately such a design requires a large internal volume for air flow and combustion.

    I rather suspect the scramjet technology group they have put together will have opened all the old projects based on ramjet technology to see if improvements in technology and materials and of course the step to scramjet might make a few previously far fetched ideas more viable.

    HVAPFSDS MBT rounds for use at long range targets would be one example... normally with APFSDS rounds they lose velocity in flight so the closer the target the better the penetration... within 2km they are at their most effective. With ramjet technology the promise was that that high velocity close in could be maintained to extend the effective range of the round to 4-5km, but with scramjet propulsion there is the promise that the rounds could actually be accelerated to higher than muzzle velocity and be effective as a very long range round that has better performance at 10km than at 1.5km.

    Obviously potential work on ATGMs and anti ship missiles and a range of other weapon types including anti satellite.


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    I have a question Garry

    Post  magnumcromagnon on Sat Jul 12, 2014 6:11 pm

    GarryB wrote:A computer can be 100% secure... simply keep it locked up in a steel safe and let no one else have access to it and keep it under 24 hour guard.

    not very useful however.

    Network access makes the computers vulnerable, but also most useful.

    Back doors like wireless connections and blue tooth add threat dimensions, but at the end of the day no network is totally secure and to make it so will slow it down and limit it to the point where it will not be useful.

    I have a question Garry, it's not related to viruses but with the creation of Zirconium scramjet cruise missile, what's the likeliness that scramjets find their way on to S-400/S-500 SAM missiles? Will it allow the missiles to have increased speed and range but with smaller dimensions, or is this just pure fantasy and not applicable to SAM missile fundamental properties?
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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  GarryB on Mon Jul 14, 2014 11:17 am

    I have a question Garry, it's not related to viruses but with the creation of Zirconium scramjet cruise missile, what's the likeliness that scramjets find their way on to S-400/S-500 SAM missiles? Will it allow the missiles to have increased speed and range but with smaller dimensions, or is this just pure fantasy and not applicable to SAM missile fundamental properties?

    It is all about design compromise. Ramjets are like jet engines and are relatively efficient... though for use in aircraft the key is re usability, so a jet aircraft is more efficient than a rocket powered aircraft for day to day flights. when the goal is to get to space however the jet just can't give enough speed so the Space Shuttle and Buran are rocket powered, which is expensive but to get to orbital speeds there really is no current alternative in terms of jet engines.

    With designs of missiles low cost becomes critical as these engines will only be used once, so rocket and ramjet and now scramjet are the three competing options. In terms of volume a ramjet requires internal space to burn the fuel, though modern Russian ramjets use that internal space to fit a rocket engine to get the missile up to speed before the ramjet is started which means multi stage rockets are not so critical, though technically it is a multi stage rocket/ramjet.

    The critical technology however is scramjet engines which in theory have no top speed, yet are fundamentally simple devices with few moving parts and no blades or shafts or "turbine" sections.

    The huge advantage of a scramjet is the ability to throttle.

    Solid fuel rockets are baked like cakes. to make them lighter they have the centre hollow, so instead of burning from one end to the other like a fuse, they burn from the centre outward, which means the walls of the rocket can be made thinner and lighter because as the rocket burns the pressure pushes out sideways is supported by the remaining fuel left to be burnt. Making the hold up the middle star shaped increases the surface area of the rocket fuel burning. the inner layer that burns first is high energy fast burning fuel generating high thrust to launch the missile and accelerate it rapidly to high speed. the next layer is slower burning that takes much longer to burn and does not accelerate the missile, it just allows it to cruise without losing speed for a few minutes.

    A missile has a peak speed where drag overcomes the thrust and so any extra thrust is largely wasted... once the missile gets to that speed then continuing to burn at full thrust is a waste of energy. Simple calculations can be made to determine how long the high energy fuel should burn with the remaining fuel being much slower burning to maintain speed for much much longer and greatly extending flight range.

    For S-400 et all the calculations are made easier because they are all ground launched and start from zero speed.

    An AAM on the other hand might be launched from a hovering helo, or a high flying MiG-31 at mach 2.6.

    Ramjets are efficient high speed jet engines where air is sucked in, fuel is added and burned and is blasted out the back generating thrust. You can throttle up and down depending on where you are and where you want to go.

    Ramjets were tested on the I-15 Polikarpov Biplane and don't need to be moving through the air at very high speed to work, though obviously they are most efficient at higher speeds.

    Solid fuel technology has improved significantly, so the Solid rocket SA-11 and SA-17 replaced the rocket ramjet SA-6 in service some time ago. For very long range however the turbojet powered Granit has been replaced by the ramjet powered Onyx... the range is shorter, but the missile is about 4 tons lighter too... the Granit is 7 tons and the Onyx is about 2.5 tons in the air launched model.

    Scramjets offer even higher speed and efficient use of fuel with the added benefit of a throttle, but the main problems remain volume and of course the need for rocket launch.

    Creating a scramjet S-400 likely wouldn't make it smaller or lighter, so I doubt they will bother, but for very long range very high speed missiles scramjet propulsion will probably be the mode of choice.

    Scramjets characteristics are still relatively unknown, so Ramjets would be the safer bet. Ramjets also allow for the missile to throttle down to around Mach 1, which could improve range dramatically.

    A scramjet is merely a ramjet that is designed so that the fuel can be burned at supersonic speed. The intake ramp on an F-16 was simplified and fixed which is what limits it to mach 2 or less. The intake ramp contracts at high speed and reduces the amount of air coming in the front of the aircraft at high speed. With its simplified fixed ramp the F-16 can't go faster than mach 2 because the air coming in is coming in too fast and would choke its engine. A scramjet on the other hand could take air coming in at any speed and still produce thrust.

    the ramjets tested on the I-15 biplane increased flight speed by something like 85km/h and could be operated at speeds as low as 100km/h.

    Like any engine aircraft combination certain configurations will be efficient, so you might find that a missile with a ramjet engine might operate best at around mach 2.5 or so, but scramjets would likely operate most efficiently above mach 5-6.

    The Russians put a scramjet engine on the nose of an SA-5 SAM which replaced the warhead and guidance section with a small scramjet engine and fuel, so the missile is launched... its solid rocket boosters burn and fall away, the main rockets burn till the missile gets to about 15,000 m altitude and mach 5, when the scramjet engine on the nose of the missile is started. It accelerates the entire missile from mach 5 to mach 6.5 and burns for about 180 seconds... in other words about 3 minutes.

    In those three minutes of burn time when the small scramjet operates the missile covers about 350km.

    The limit of a turboprop engine is the speed of sound, the limit of a turbojet engine is about mach 3 in conventional mode. The limit of a ramjet engine is mach 5-6 or so. The limit for a scramjet is heat. If you had materials that could take the heat and speed a scramjet can take you to orbital speeds... into space... though in space it would no longer function of course.


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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  Mike E on Mon Jul 14, 2014 5:05 pm

    Not in any way do I doubt Scramjets advantages. However, they still remain relatively untested, and aren't in service with anyone quite yet. Also, the minimum speed requirement of ~ Mach 5 isn't exactly a good thing. A Scramjet missile would need a very large and powerful solid-rocket first stage. 

    GarryB, do you know why SAMs never implement "Aero-spikes" as found on the Trident series of ICBMs? They are said to improve aerodynamics by up-to/over 50%, which would result in a considerably greater range.

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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  etaepsilonk on Mon Jul 14, 2014 6:18 pm

    Mike E wrote:
    Scramjets characteristics are still relatively unknown, so Ramjets would be the safer bet. Ramjets also allow for the missile to throttle down to around Mach 1, which could improve range dramatically.

    Is that so?

    From what I know, it's the other way around, efficiency increases with ram pressure, which is proportionate to speed. Correct me if I'm wrong  Wink


    "GarryB, do you know why SAMs never implement "Aero-spikes" as found on the Trident series of ICBMs? They are said to improve aerodynamics by up-to/over 50%, which would result in a considerably greater range."

    Dunno exactly, but maybe high alfa angles have something to do with it?

    ------------------



    To Garryb:
    "Creating a scramjet S-400 likely wouldn't make it smaller or lighter, so I doubt they will bother, but for very long range very high speed missiles scramjet propulsion will probably be the mode of choice."

    I'd like to add that current scramjets able to emulate the performance of 48N6's/40N6's rocket engines are not yet available, even prototypes.
    The best performing S-J, X-51 "waverider", goes only to about mach 6, while even middle tier s-400 missile has a burnout speed of about 8 mach, quite a significant difference. And I'm not even talking about 40N6 with ~12 mach Smile
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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  Mike E on Mon Jul 14, 2014 10:26 pm

    Yes and no, while Scramjets have been tested, they've never been put to use.

    Scramjets do use a lot of use, with the benefit being speed. I would guess Ramjets are less efficient around Mach 5 (Scramjet speed), but more so at lower speeds (for obvious reasons) (I need a second opinion on this, correct me if I'm wrong).

    Could be, I'm not sure. From what I've read, Spikes wouldn't be a problem at high angles of attack because of their small size and surface area.

    Scramjets aren't "there yet", but when they are, you can expect big things.
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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  GarryB on Tue Jul 15, 2014 4:40 am

    Also, the minimum speed requirement of ~ Mach 5 isn't exactly a good thing. A Scramjet missile would need a very large and powerful solid-rocket first stage.

    There are no hard limits of speed for scramjets... the SA-5 test just started testing at mach 5 because that is the normal flight speed of the SA-5 so that is when it started operating.

    The engines in the SR-71 are a good example of what can be expected.

    they work as standard turbojets for takeoff and landing, but as they accelerate to high speed bypass air that is sucked in the intake but goes around the outside rather than through the engine is increased. This air going around the engine is called bypass air, just like on a turbofan, engine, but in this case when the SR-71 is flying at mach 3.5 almost no air is flowing through its turbojet engines which produce almost no thrust. The bypass air has fuel added and operates like a ramjet and produces the thrust to propel the aircraft.

    Having a variable cycle engine is likely the future.

    In fact an onboard store of fuel and oxygen and the ability to close the intakes could be used for a space plane.

    Use normal jet propulsion to take off from a runway with air sucked in the intakes and fuel used with the air coming in the intakes. Climb and accelerate to supersonic speed and close off the turbojet engine with bypass air acting like a scramjet with air still coming in the intakes and accelerate to mach 26... turn to a flight path to take you out of the atmosphere and close off the intakes and start feeding the O2 and burn it with the fuel and you pretty much have a rocket plane. So turbojet, scramjet, rocket propulsion.

    GarryB, do you know why SAMs never implement "Aero-spikes" as found on the Trident series of ICBMs? They are said to improve aerodynamics by up-to/over 50%, which would result in a considerably greater range.

    Not the best solution... an aerospike is used on missiles with rounded noses of poor aerodynamic design for supersonic flight. Trident has a round nose because of the design constraints to pack as much missile in as small a tube as possible so rather than an efficient long pointy nose is has a stumpy rounded nose which would be aweful for supersonic flight.

    Another application is IR guided SAMs and AAMs because the IR optical sensor is most efficient with a rounded nose which greatly increases nose induced drag.

    The example would be Igla with its aerospike to improve performance without compromising the shape of the nose optical port.

    In comparison the Mistral has a pointed nose which effects its IR sensitivity and performance.

    Very simply the Russians went for a good optical sensor performance and good flight performance,while the French compromised IR sensor performance for aerodynamic performance.

    From what I know, it's the other way around, efficiency increases with ram pressure, which is proportionate to speed. Correct me if I'm wrong

    It is a bit like a car... in top gear you move most efficiently using the least fuel... the worst performance is low speed accelerating, the best performance is top speed cruising with a low throttle setting to maintain speed by countering drag.

    I'd like to add that current scramjets able to emulate the performance of 48N6's/40N6's rocket engines are not yet available, even prototypes.
    The best performing S-J, X-51 "waverider", goes only to about mach 6, while even middle tier s-400 missile has a burnout speed of about 8 mach, quite a significant difference. And I'm not even talking about 40N6 with ~12 mach

    Very true, but the key is that scramjets are in their infancy and have enormous potential.... in a range of applications.

    I would guess Ramjets are less efficient around Mach 5 (Scramjet speed), but more so at lower speeds (for obvious reasons) (I need a second opinion on this, correct me if I'm wrong).

    Ramjets choke on supersonic air, just like turbojets do. The fastest flying turbojet engine is the engine in the MiG-31 where all the thrust is derived from the turbojet engine. The problem is that as you approach Mach 3 the incoming air needs to be slowed down so when it goes through the engine in the hot section where fuel is added it is subsonic so the fuel burns properly. To achieve this the intake narrows and reduces the airflow into the engine, which slows it down to subsonic speed. Of course the limitation of speed of the engine is how fast it can push this air and the burnt fuel out the back... the speed it pushes it out determines how much thrust is produced... if the air through the hot section becomes supersonic it will flameout and stall and the air blown out the rear will greatly lose heat and energy and thrust will go down.

    It is the same for a ramjet... if the air going into the hot section becomes supersonic it will flame out and stall and thrust will be lost.

    Most ramjets are efficient in the mach 3-4 range but not much more... they still need a certain volume of air flowing through them to generate thrust to maintain flight.

    With a scramjet the airflow is still controlled but can be allowed to go through much faster including supersonic or faster through the hot section meaning a lot more thrust and much higher speed.

    the limitations on scramjets is heat... the insides can melt and the external surfaces of the aircraft can melt due to the high temperatures generated in high speed flight.


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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  magnumcromagnon on Tue Jul 15, 2014 6:05 am

    GarryB wrote:The limitations on scramjets is heat... the insides can melt and the external surfaces of the aircraft can melt due to the high temperatures generated in high speed flight.

    What's the likeliness that Space Shuttle-style heat tiles make their way on to scramjet vehicles?
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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  Mike E on Tue Jul 15, 2014 6:31 am

    Thank you for all that info! 

    I simply mean that Scramjets have to be accelerated in order to function. This isn't that big of a problem for missiles, but is for larger/heaver planes etc. 

    The SR-71 really was a revolution, that engine technology was way ahead of its time. (Thank you Kelly!!!)

    I completely agree, we will be seeing much more in the variable cycle area. (Just to let you know, I know the basics of Turbojets and jet engines in general. I used to know a TON on Scramjets, but it all came out of me.)

    Ok, thank you for answering that for me. I guess it is more of a stop-gap solution than anything else. If I remember right, India is said to have a better solution in which the rocket somehow ionizes (?) the air in front of it, supposedly increase aero properties by ~45% .

    That sounds reasonable, especially when Scramjets are "popular".

    Heck, I feel Ramjets are still undervalued! (Yes I know, Scramjets are basically the same thing.)

    That's is one advantage of Scramjets, they probably don't create as much drag. (By not slowing down the incoming air, causes air around the engine to "reroute".

    Heat will always be an issue, but there are many ways of (for the most part) overcoming it. Look at MIRVs, they travel at Mach 10! (Albeit with heat shields.)

    (I found the Indian aero technology, here it is; http://www.domainb.com/aero/mil_avi/miss_muni/20080910_Indian_technology.html )
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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  Mike E on Tue Jul 15, 2014 6:33 am

    magnumcromagnon wrote:
    GarryB wrote:The limitations on scramjets is heat... the insides can melt and the external surfaces of the aircraft can melt due to the high temperatures generated in high speed flight.

    What's the likeliness that Space Shuttle-style heat tiles make their way on to scramjet vehicles?

    Very plausible, if not, engineers will find a better solution.

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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  etaepsilonk on Tue Jul 15, 2014 10:57 am

    GarryB wrote:Not the best solution... an aerospike is used on missiles with rounded noses of poor aerodynamic design for supersonic flight. Trident has a round nose because of the design constraints to pack as much missile in as small a tube as possible so rather than an efficient long pointy nose is has a stumpy rounded nose which would be aweful for supersonic flight.

    Another application is IR guided SAMs and AAMs because the IR optical sensor is most efficient with a rounded nose which greatly increases nose induced drag.

    The example would be Igla with its aerospike to improve performance without compromising the shape of the nose optical port.

    In comparison the Mistral has a pointed nose which effects its IR sensitivity and performance.

    Very simply the Russians went for a good optical sensor performance and good flight performance,while the French compromised IR sensor performance for aerodynamic performance.

    Yeah, seems true enough Smile


    ----------------------------
    magnumcromagnon wrote:
    GarryB wrote:The limitations on scramjets is heat... the insides can melt and the external surfaces of the aircraft can melt due to the high temperatures generated in high speed flight.

    What's the likeliness that Space Shuttle-style heat tiles make their way on to scramjet vehicles?

    Eh, I think space shuttle's (and other space carriers', actually) tiles are built for quite a different purpose. That is, to be used not in flight, but in descent.
    And that descent is rough- flying at near 90 degrees AoA while slowing down from mach 20 to mach 2-3. I don't think the near future scramjet vehicles need that kind of strength yet.
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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  Mike E on Wed Jul 16, 2014 6:35 am

    Does anyone have any thoughts on that Indian aerodynamic feature? 

    "Agni III, which is India's longest-range missile with a capability of striking targets 3,500 km away, may now have an extended range of around 5,000 km thanks to a unique solution discovered by Indian scientists at the prestigious Indian Institute of Science (IISc) here. The technology will increase the range of not just missiles but also other satellite launch vehicles.
    The technology also has the exciting possibility of reducing the risk of occurrence of a Columbia space shuttle-type of tragic accident.
    The enhanced range of an Indian re-entry vehicle or missile will now be due to a special-purpose coating of chromium metal applied to the blunt nose cone of missiles and launch vehicles, for which international patents have been sought for by the team of IISc scientists.

    ''Objects such as missiles fly at hypersonic velocities which are more than five times the speed of sound and encounter atmospheric drag because of friction. The chromium coating works by adding temporary heat and pushing the stagnating gas away to create an easier path,'' G Jagadeesh, an assistant professor at the IISc here said.
    The findings of the IISc team, which also includes Vinayak Kulkarni of IIT (Guwahati) and GM Hegde, E Arunan and KPJ Reddy, have been reported in the latest issue of the Physics of Fluids journal published by the American Institute of Physics.
    Laboratory experiments have shown that atmospheric drag because of the coating fell by 47% and Jagadeesh said a ''conservative estimate'' was that this would result in range going up by at least 40%.
    ''The measurements show about 47% reduction in the drag coefficient for a 60° apex angle blunt cone in a Mach 8 flow of 3.4  MJ/kg specific enthalpy,'' reads an extract from the article in the journal.
    Scientists say the breakthrough also has potential to avert disasters of the type that struck space shuttle Columbia in 2003, which resulted in the death of seven astronauts, including Indian-born astronaut Kalpana Chawla. The shuttle burned out as it was re-entering the earth's atmosphere as there were problems it's thermal protection system.
    The special-purpose coating developed at the IISc could likely replace the tiles and panels which currently protect orbiters against extreme heat during re-entry into the atmosphere.
    ''The coating evaporates once the object has re-entered the atmosphere. This novel method is path-breaking because additional energy is not required to reduce drag; objects which travel into space need to carry a much lower fuel load,'' Jagadeesh said."

    - From domain-b, I posted the complete address earlier.

    Anyway, I think it seems like a great idea. These "coatings" could be applied to all Russian SAMs, and really help them "reach out" to farther distances.  russia 
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    Re: Ramjet vs Scramjet propulsion SAMs

    Post  GarryB on Wed Jul 16, 2014 12:45 pm

    What's the likeliness that Space Shuttle-style heat tiles make their way on to scramjet vehicles?

    Ablative tiles could be useful for one use systems like rockets, but for reusable craft like the shuttle they are a pain in the backside... after every flight they need to be very carefully examined for wear or cracks with old tiles replaced.

    A better solution would be to pump slush hydrogen fuel through the aircraft skin... it is very cold and would take the heat out of any surface... very much the same as if you throw a plastic bottle on the fire it will quickly melt and catch fire itself. Now take a similar bottle and fill it with water and throw it on the fire... the heat from the fire is absorbed by the water so the plastic does not get hot enough to melt because the water draws the heat away from the plastic.

    I simply mean that Scramjets have to be accelerated in order to function. This isn't that big of a problem for missiles, but is for larger/heaver planes etc.

    Certainly with a scramjet... with a heat limit rather than a speed limit the faster you can accelerate it the better... a rocket engine will accelerate it faster than it can accelerate on its own.

    Even a pulse detonation engine can operate from stationary, but becomes rather more efficient as the aircraft moves faster. It is just like gears and internal combustion engines... very low gears and cold engines reduce efficiency and performance.

    Heck, I feel Ramjets are still undervalued! (Yes I know, Scramjets are basically the same thing.)

    A scramjet is a type of ramjet... think of it in terms of turbojets... an old end of WWII turbojet engine is still a turbojet engine. Comparing it to a modern turbojet engine and you could almost say they are different engines but the basic functionality is different. Without a variable ramp air intake a turbojet from a late WWII plane would stall at supersonic speed.. the same with a ramjet and a scramjet.

    Obviously ramjets are incredibly simple, scramjets are slightly more complex, but until the ramjet is operating at very high speed the combustion will be subsonic anyway so a scramjet and a ramjet will be identical. It is only when the ramjet loses thrust and the scramjet continues to burn fuel supersonically and generates rather more thrust than any ramjet can generate that the differences become obvious.

    That's is one advantage of Scramjets, they probably don't create as much drag. (By not slowing down the incoming air, causes air around the engine to "reroute".

    The Scramjet at any speed can have the air intake wide open which means higher airflow, higher exhaust speed and rather more thrust.

    Heat will always be an issue, but there are many ways of (for the most part) overcoming it. Look at MIRVs, they travel at Mach 10! (Albeit with heat shields.)

    The period of time they travel at mach 10 is fairly short as they fall through the atmosphere... if we assume the atmosphere is only significant in terms of drag up to about 50km then we are talking about less than 20 seconds of reentry.

    And that descent is rough- flying at near 90 degrees AoA while slowing down from mach 20 to mach 2-3. I don't think the near future scramjet vehicles need that kind of strength yet.

    Good point... the space shuttle uses its wings and lower surface area as a sort of aerobrake, so it does rapidly heat up. Importantly the angle of entry into the atmosphere is critical... too steep and it gets too hot and you burn up. Not steep enough and you skip like a stone on flat water back up into space.

    For high speed flight there are areas of the airframe that will be subjected to continuous friction heat... a Mach 2.86 the canopy of the MiG-31 can get to 70 degree Celsius... other external parts like the wing root get much hotter and cannot be made of Aluminium or it will melt.

    ''The coating evaporates once the object has re-entered the atmosphere. This novel method is path-breaking because additional energy is not required to reduce drag; objects which travel into space need to carry a much lower fuel load,'' Jagadeesh said."

    If the coating evapourates on reentry then how can it operate as a substitute for heat tiles?

    I am skeptical and would want rather more information directly from the people developing the technology.


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    Mike E

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    scramjet vs ramjets

    Post  Mike E on Wed Jul 16, 2014 5:08 pm

    GarryB wrote:
    What's the likeliness that Space Shuttle-style heat tiles make their way on to scramjet vehicles?

    Ablative tiles could be useful for one use systems like rockets, but for reusable craft like the shuttle they are a pain in the backside... after every flight they need to be very carefully examined for wear or cracks with old tiles replaced.

    A better solution would be to pump slush hydrogen fuel through the aircraft skin... it is very cold and would take the heat out of any surface... very much the same as if you throw a plastic bottle on the fire it will quickly melt and catch fire itself. Now take a similar bottle and fill it with water and throw it on the fire... the heat from the fire is absorbed by the water so the plastic does not get hot enough to melt because the water draws the heat away from the plastic.

    I simply mean that Scramjets have to be accelerated in order to function. This isn't that big of a problem for missiles, but is for larger/heaver planes etc.

    Certainly with a scramjet... with a heat limit rather than a speed limit the faster you can accelerate it the better... a rocket engine will accelerate it faster than it can accelerate on its own.

    Even a pulse detonation engine can operate from stationary, but becomes rather more efficient as the aircraft moves faster. It is just like gears and internal combustion engines... very low gears and cold engines reduce efficiency and performance.

    Heck, I feel Ramjets are still undervalued! (Yes I know, Scramjets are basically the same thing.)

    A scramjet is a type of ramjet... think of it in terms of turbojets... an old end of WWII turbojet engine is still a turbojet engine. Comparing it to a modern turbojet engine and you could almost say they are different engines but the basic functionality is different. Without a variable ramp air intake a turbojet from a late WWII plane would stall at supersonic speed.. the same with a ramjet and a scramjet.

    Obviously ramjets are incredibly simple, scramjets are slightly more complex, but until the ramjet is operating at very high speed the combustion will be subsonic anyway so a scramjet and a ramjet will be identical. It is only when the ramjet loses thrust and the scramjet continues to burn fuel supersonically and generates rather more thrust than any ramjet can generate that the differences become obvious.

    That's is one advantage of Scramjets, they probably don't create as much drag. (By not slowing down the incoming air, causes air around the engine to "reroute".

    The Scramjet at any speed can have the air intake wide open which means higher airflow, higher exhaust speed and rather more thrust.

    Heat will always be an issue, but there are many ways of (for the most part) overcoming it. Look at MIRVs, they travel at Mach 10! (Albeit with heat shields.)

    The period of time they travel at mach 10 is fairly short as they fall through the atmosphere... if we assume the atmosphere is only significant in terms of drag up to about 50km then we are talking about less than 20 seconds of reentry.

    And that descent is rough- flying at near 90 degrees AoA while slowing down from mach 20 to mach 2-3. I don't think the near future scramjet vehicles need that kind of strength yet.

    Good point... the space shuttle uses its wings and lower surface area as a sort of aerobrake, so it does rapidly heat up. Importantly the angle of entry into the atmosphere is critical... too steep and it gets too hot and you burn up. Not steep enough and you skip like a stone on flat water back up into space.

    For high speed flight there are areas of the airframe that will be subjected to continuous friction heat... a Mach 2.86 the canopy of the MiG-31 can get to 70 degree Celsius... other external parts like the wing root get much hotter and cannot be made of Aluminium or it will melt.

    ''The coating evaporates once the object has re-entered the atmosphere. This novel method is path-breaking because additional energy is not required to reduce drag; objects which travel into space need to carry a much lower fuel load,'' Jagadeesh said."

    If the coating evapourates on reentry then how can it operate as a substitute for heat tiles?

    I am skeptical and would want rather more information directly from the people developing the technology.

    I agree on your second point, about using rockets to get the Scramjet "up to speed". Hopefully variable cycle engines will solve this problem soon enough. 

    Yeah, what I meant to say is that Ramjets have never been fully utilized like Turbofans (for example). (I knew the differences already, but maybe other people will learn.)

    That is true, but MIRVs also have to travel though the thick atmosphere, unlike missiles which might have a booster to get it "up high".
    .
    I don't see it replacing heat tiles, as they would have to reapply after every flight. However, I do see its potential when it comes to reducing drag, which is almost invaluable. (Agni III, which is India's longest-range missile with a capability of striking targets 3,500 km away, may now have an extended range of around 5,000 km thanks to a unique solution discovered by Indian scientists at the prestigious Indian Institute of Science (IISc) here.) Those 1500 km are a huge deal.

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